This invention relates to egg inspecting apparatuses with which inferior or defective eggs can be detected without breaking the eggs.
In conventional egg inspecting apparatuses operating to detect blood-containing eggs (hereinafter referred to as "blood eggs" when applicable), a light having a wavelength of 575 m.mu. (hereinafter referred to as "a 575 m.mu. light or an absorptive light" when applicable) which is appreciably absorbed by blood and a light having a wavelength of 600 m.mu. (hereinafter referred to as "a 600 m.mu. light or a non-absorptive light" when applicable) which are not appreciably absorbed by blood are applied to an egg to be inspected, and the two lights transmitted through the egg are compared with each other to determine the presence or absence of blood in the egg.
However, it is not logical to determine the presence or absence of blood merely by comparing the intensities of the two lights transmitted through the egg, because the intensities of light transmitted through eggs vary depending on the optical properties of the eggs such as the variations in thickness and color of the shells thereof. In order to solve this problem, in the conventional egg inspecting apparatus, the level of a light detection signal obtained by detecting the 600 m.mu. light transmitted through an egg is maintained fixed irrespective of the optical property of the egg, and the level of a light detection signal obtained by detecting the 575 m.mu. light passed through the egg is determined relative to the level of the 600 m.mu. light thus maintained fixed, thereby determining the presence or absence of blood in the egg.
For this purpose, photomultipliers are provided respectively for receiving the absorptive light and the non-absorptive light, and the level of the detection signal of the photomultipler provided for the non-absorptive light is maintained fixed by the use of a compensation circuit. On the basis of the level of the detection signal thus maintained fixed, the level of the detection signal of the photomultiplier tube provided for the absorptive light is determined. Since the photomultiplier tube has higher sensitivity than other photosensitive elements, it is advantageous in that, for instance, the provision of an amplifier is unnecessary, and the intensity of a light source may be lower.
However, the photomultiplier tube has an inherent difficulty in that its linearity range is small. A sensitivity characteristic of the photomultiplier tube is as indicated by the solid line in FIG. 1, and therefore in the inspection of eggs with brown shells (hereinafter referred to as "brown eggs" when applicable) the sensitivity of the photomultiplier tube should be increased as indicated by the broken line in FIG. 1. Under this condition, the outputs of the photomultiplier tube produced by lights L.sub.1 and L.sub.2 in the inspection of a normal egg with a white shell and an egg containing a slight amount of blood fall within the saturation range of the characteristic curve indicated by the broken line, and, therefore, it is impossible to detect even blood eggs. In order to solve this problem, a compensation circuit is provided in the conventional egg inspecting apparatus in such a manner that the sensitivity of the photomultiplier tube where the intensity of a light passed through an egg is high, that is, where a light passed through a normal egg with white shell falls in the linearity range.
Defective eggs include so-called "green eggs" which are eggs affected with bacteria as well as blood eggs, addled eggs and turbid eggs which can be detected by the use of visible light as was described above. The bacteria are regarded to be low-temperature bacteria such as "pseudomonas fluorescences". When such bacteria have propagated in an egg, the albumen of the egg can be visually observed to be green. However, when the propagation of bacteria in an egg is slight, it is impossible to visually detect whether or not the egg is affected with the bacteria even if the egg is broken.
The bacteria described above are not poisonous and are not bacilli but are well known as decomposing bacteria. It has been determined in the United States of America and also in Japan that green eggs are not fit for use as food.
However, conventional green egg detection methods are applicable only to eggs in which the propagation of bacteria has advanced remarkably. Accordingly, there has been a strong demand for the provision of an egg inspecting apparatus capable of positively detecting not only eggs in which the degree in propagation of bacteria is remarkable, but also eggs in which the degree in propagation of bacteria is slight.
As is apparent from the above description, the conventional egg inspecting apparatuses are directed only to the detection of blood eggs, and addled or turbid eggs originated from blood, or only to green eggs. That is, heretofore, there has been no egg inspecting apparatus which can quickly and positively detect all of the defective eggs including blood eggs, addled or turbid eggs, and green eggs.